The present invention generally relates to visual effect implementations for the images on the screen of a display device, and more specifically to a method and apparatus for displaying a dissolving image by providing sequential images to form the dissolving transition on the screen.
On the screen of a display device, a computer can display an image that appears or disappears gradually as a fade-in or fade-out effect. Each of the visual effects, namely dissolve effect, is achieved by manipulating the picture elements, or pixels, of the image.
An array of a large number of pixels displayed at respective intensities forms an image on the display screen. The information on the pixel intensities is supplied through video signals by the computer. The computer holds values for the respective pixels in a storage device, from which the pixel values are read in a sequence to produce the video signals.
The display device, typically comprising a cathode ray tube (CRT), performs raster scans at a certain repetition rate to display images on its screen. This repetition rate, or screen scan rate, must be high enough for displaying flickerless images and is typically selected to greater than 50 Hz according to the human eye nature. The pixel values of images to be displayed on the screen, therefore, should be read from the storage device at the same rate to create the video signals for the display.
The computer device may produce a dissolving image on the screen by providing the display with the video signals for displaying a series of images that vary their intensities progressively based on their respective phases in the dissolving process. The intensities of the images can be modified by weighting their pixel values. Therefore, the computer may repeatedly multiply the pixel values by a weight while progressively increasing or decreasing the weight image by image. Then the video signals can be produced based on the weighted pixel values to display the images sequentially on the display screen to form the dissolving image.
Enhanced processing powers of Central Processing Units (CPUs) and peripheral devices in recent years allow computer devices to provide various computer graphics in a realistic fashion, thereby attracting the users. However, computers, such as those for personal use, are still deficient in processing speeds, and thus are limited in capabilities for rendering images including those in dissolving transitions. Especially larger size images represented by a larger amount of pixels require longer processing time for aforementioned weighting procedures, so that the frame rates in displaying the sequential images are deteriorated, resulting in a discontinuous dissolve effect, or a dissolving transition in an undesirable stepping manner, on the display screen.
It is the primary object of the present invention to provide a method and apparatus capable of smoothly dissolving an image on a display screen.
In accordance with the invention, sequential images to be successively displayed on the screen to form the dissolving transition of the objective image are generally provided by applying a progressively-varied weight to the pixel values of the objective image, which is composed of a two-dimensional pixel array.
For shortening the time required to create the respective images forming the dissolving transition, the pixels of the objective image, according to the invention, are divided into a plurality of groups in such a manner that the pixels in each group are dispersed in the image. Then one of the pixel groups is selected and all the pixel values of the selected group are read from first storage means to multiply them by a weight respectively. The resultant weighted pixel values are stored respectively in the storage locations, corresponding to the selected pixel group, within second storage means. The selecting, reading, multiplying, and storing procedures are repeated, wherein the respective pixel groups are selected cyclically and the weight is increased or decreased gradually as the repetition of the procedures progresses. In parallel with this repetition, the weighted pixel values are cyclically read from the second storage means, in each reading cycle the pixel values corresponding to the pixel groups being read in a predetermined order to display one of the sequential images on the screen.
According to the present invention, the respective images to form the dissolving transition are created in shorter time periods due to the reduced number of pixels to be weighted in each image. Therefore, the images can be displayed at higher frame rates, resulting in a smooth dissolve effect on the display screen.